Project Summary The objective of this proposal is to determine how angiogenin (ANG)-induced transfer RNA (tRNA)-derived small non-coding (snc) RNAs reprogram protein translation to promote the survival of cells exposed to adverse conditions. Our central hypothesis is that ANG-induced tiRNAs function to enhance the expression of pro- growth and pro-survival proteins to promote tumorigenesis and prevent neuronal death. This is based upon our own preliminary data showing that ANG selectively cleaves tRNAs to produce bioactive fragments (i.e., tiRNAs) that use multiple mechanisms to inhibit translation initiation and induce stress granule assembly. This requires interactions with translational regulatory proteins YB1 and CNBP. The rationale for the proposed research is that, once we know how tiRNAs re-program protein translation to promote cell survival, we will be able to modulate these events to treat cancer and neurodegenerative disease. We will test our central hypothesis by the completion of three specific aims: AIM 1. To elucidate the scope of tiRNA-mediated translational repression. Our working hypothesis is that distinct classes of tiRNAs bind to the nucleic acid- binding proteins to target translation initiation, elongation, and/or recycling machinery. AIM 2. To determine how terminal oligoguanine (TOG)-containing tiRNAs modulate 5'terminal oligopyrimidine (TOP) translation. Our working hypothesis is that tiRNA:YB1 and tiRNA:CNBP complexes target 5'TOP-containing transcripts that encode ribosomal proteins and translation factors to modulate protein synthesis in response to stress. AIM 3. To determine how G4 structures modulate tiRNA/DNA function. Our working hypothesis is that tiRNA/DNAs assembly G-quadruplex (G4) structures that are critical for binding to YB1 and CNBP and that modulation of G4 assembly may be a way to modulate their biological activities. These aims will be accomplished by determining the mechanism by which different classes of tiRNAs inhibit translation, identifying the composition of tiRNA ribonucleoprotein complexes, and identifying tiRNA target transcripts. We will also determine how tiRNAs modulate the ability of YB1 and CNBP to repress and promote mRNA translation with a special emphasis on TOP mRNAs that regulate general protein translation. Finally, we will determine whether CNBP functions as a G4 chaperone to modulate the structure of tiRNAs and test the hypothesis that Li+- mediated disruption of G4 structures can modulate the biological function of tiRNAs. The contribution of the proposed research will be to determine how tiRNAs, or their DNA analgues, promote the growth and survival of cells involved in the pathogenesis of cancer and neurodegenerative disease. This contribution is significant because it provides a molecular basis for the development of pharmacologic strategies to prevent tiRNA- mediated tumor growth or promote tiRNA-mediated motor neuron survival. The proposed research is innovative because it focuses on the downstream effector of ANG-induced tRNA cleavage and attempts to provide a proof of mechanism needed to develop these sncRNAs into therapeutics.